!pip install -U transformers
!pip install sentencepiece

from transformers import PegasusTokenizer
tokenizer = PegasusTokenizer.from_pretrained('google/pegasus-large')

ImportError                               Traceback (most recent call last)

<ipython-input-7-12d68b5e397b> in <module>()
      1 from transformers import PegasusTokenizer
----> 2 tokenizer =    PegasusTokenizer.from_pretrained('google/pegasus-large')

/usr/local/lib/python3.6/dist-packages/transformers/utils/dummy_sentencepiece_objects.py in from_pretrained(self, *args, **kwargs)
     54     @classmethod
     55     def from_pretrained(self, *args, **kwargs):
---> 56         requires_sentencepiece(self)
     57 
     58 

/usr/local/lib/python3.6/dist-packages/transformers/file_utils.py in requires_sentencepiece(obj)
    459     name = obj.__name__ if hasattr(obj, "__name__") else obj.__class__.__name__
    460     if not is_sentencepiece_available():
--> 461         raise ImportError(SENTENCEPIECE_IMPORT_ERROR.format(name))
    462 
    463 

ImportError: 
PegasusTokenizer requires the SentencePiece library but it was not found in your environment. Checkout the instructions on the
installation page of its repo: https://github.com/google/sentencepiece#installation and follow the ones
that match your environment.